(Per)fluoropolyethers (PFPE) are fluorinated polymers comprising a fully or partially fluorinated polyoxyalkylene chain that contains recurring units having at least one catenary ether bond and at least one fluorocarbon moiety. The most widespreadly known PFPE can be obtained by homopolymerization of hexafluoropropylene oxide (HFPO) or 2,2,3,3-tetrafluorooxetane and by photooxidation of tetrafluoroethylene (TFE) and/or hexafluoropropylene (HFP).
PFPE are in the form of oils under normal conditions and at relatively high or low temperature and, thanks to their stability, inertness, low volatility and outstanding rheological and tribological properties, they are useful in a variety of applications, mainly lubricant applications, wherein harsh conditions are reached (e.g. high temperatures, friction, etc . . . ).
One of the main problems in the synthesis of PFPE lies in the difficulty of obtaining PFPE with high molecular weight. Indeed, the currently available methods of synthesis allow obtaining PFPE having an average number molecular weight (Mn) usually ranging from 400 and 5,000. PFPE with (Mn) ranging from 3,500-5,000 are usually isolated from mixtures comprising PFPE with lower molecular weights. The isolation of monofunctional PFPE with high molecular weight is particularly difficult on an industrial scale and usually provides low yields.
There is therefore the need to provide a method for manufacturing PFPE having a wide range of molecular weights, in particular high molecular weights, said method being conveniently implementable on an industrial scale and allowing to isolate monofunctional PFPE with satisfactory yields.
PFPE can be divided into non-functional and functional; the former comprise a PFPE chain whose ends bear (per)haloalkyl groups, while the latter comprise a PFPE chain wherein at least one end comprises a functional group. Among functional PFPE, PFPE alcohols, in particular those terminating with one or two —CH2OH groups, can be used as valuable intermediates for the manufacture of other PFPE. Indeed, the hydroxy group can react as a nucleophile or can be transformed into a leaving group that undergoes nucleophilic displacement.
BRIZA, Thomas, et al. Electrophilic polyfluoroalkylating agents based on sulfonate esters. Journal of Fluorine Chemistry. 2008, vol. 129, p. 235-247. disclose the synthesis of several sulfonate esters that can be used as electrophilic agents in the manufacture of a variety of compounds, including ethers from fluorinated and non-fluorinated alcohols. However, the reaction of such sulfonate esters with PFPE alcohols is neither disclosed nor suggested.
The following articles:                RAKHIMOV, A. V., et al. New Catalytic Synthesis of Polyfluoroalkyl Chlorosulfites. Russian Journal of General Chemistry. 2004, vol. 74, no. 5, p. 799-800.        RAKHIMOV, A. V., et al. Synthesis of di(polyfluoroalkyl)ethers. Russian Journal of General Chemistry. 2004, vol. 77, no. 4, p. 1561-1563. disclose the synthesis of polyfluoroalkyl chlorosulfites and their subsequent conversion to ethers. Such ethers comprise a connecting hydrogenated spacer of formula —CH2OCH2— between two fluorinated segments. However, the fluorinated starting materials used in the preparation of the chlorosulfites disclosed in the examples are not PFPE alcohols. When the Applicant tried to prepare chlorosulfites of PFPE diols following the teaching of the above articles, the desired chlorosulfite derivative was not obtained.        
TONELLI, Claudio, et al. Linear perfluoropolyethers difunctional oligomers: chemistry, properties and applications. Journal of Fluorine Chemistry. 1999, vol. 95, p. 51-70. discloses the conversion of PFPE diols of formula:HOCH2—CF2(OCF2)q(OCF2CF2)pOCF2—CH2OHcommercially known as Fomblin® Z DOL,
and of corresponding ethoxylated derivatives of formula:H(OCH2CH2)nOCH2—CF2(OCF2)q(OCF2CF2)pOCF2—CH2O(CH2CH2O)nH,into the corresponding nonaflate and tosylate esters respectively. However, the article refers only to the reaction of nonaflate esters with NaI to provide the corresponding diiodide derivatives.
TONELLI, Claudio, et al. Perfluoropolyether functional oligomers: unusual reactivity in organic chemistry. Journal of Fluorine Chemistry. December 2002, vol. 118, no. 1-2, p. 107-121. reports and discusses the reactivity of functional PFPEs having hydroxy terminal groups and sulfonate terminal groups.
SCICCHITANO, Massimo, et al. Cyclic acetals of fluorinated polyether alcohols. Journal of Fluorine Chemistry. 1999, vol. 95, p. 97-103. disclose the reaction of Fomblin® Z DOL PFPE with dihalomethanes to provide a dihalogenated derivative which may react with Fomblin® Z DOL PFPE to provide polymers comprising PFPE segments and hydrogenated segments of formula —CH2OCH2OCH2—. However, such segments are not stable and undergo hydrolysis under acid conditions.
EP 0538827 A (AUSIMONT SPA) 28 Apr. 1993 relates to a method for separating mono-, bi- and non-functional PFPEs, including PFPEs having CH2OH terminations, by column chromatography.
EP 1614703 A (SOLVAY SOLEXIS SPA) 11 Jan. 2006 relates to a method for the separation of bifunctional PFPEs having —CH2OH terminations from mixtures comprising the corresponding monofuntional compounds by absorption/desorption on a solid phase.
WO 2013/606558 discloses a process for increasing the content of bifunctional specied in PFPE mixtures having, inter alia, hydroxy terminations, by absorption/desorption on a stationary phase using a supercritical fluid and a polar solvent.
Polymers comprising both (per)fluoropolyoxyalkylene segments and fully hydrogenated segments are also known and can be used instead of PFPE in applications in which PFPE would be outperforming and/or too expensive, for example in the field of lubrication. For example, EP 2089443 B (SOLVAY SOLEXIS S.P.A.) 19 Aug. 2009 discloses non-functional block copolymers comprising PFPE blocks and blocks deriving from one or more homopolymerizable olefins. Such block copolymers can be manufactured by means of a process comprising the reaction of a peroxidic PFPE with one or more homopolymerizable olefins by radical route, thermal treatment and neutralization.
WO 2010/057691 A (SOLVAY SOLEXIS SPA) 27 May 2010 discloses, inter aka, bifunctional hydrofluoroalcohols comprising a plurality of (per)fluoropolyether (PFPE) segments joined together by —O—Rh—O— segments, wherein Rh is a hydrocarbon-based chain. For instance, Example 3 discloses a compound having formula:HOCH2CH2CH2CH2—OCF2—Rf—CF2O—CH2CH2CH2CH2O—(CF2—Rf—CF2O—C H2CH2CH2CH2O)nHwhile example 8 discloses a compound of formula:HOCH2CH2CH2—OCF2—Rf—CF2O—CH2CH2CH2O(CF2—Rf—CF2O—CH2CH2CH2O)nHwherein Rf is a PFPE chain.
Such compounds are obtained by reaction of a difunctional alkylating compound with a carbonyl derivative of a PFPE in the presence of a source of fluoride anion, followed by hydrolysis of the resulting product.
The need of finding novel polymers comprising PFPE segments and fully hydrogenated segments is still felt. In particular, there is the need to provide functional polymers comprising PFPE segments, said polymers having a wide range of molecular weights and, at the same time, being endowed with chemico-physical properties not significantly different from those of known PFPE polymers having the same molecular weight.
It would also be desirable to provide methods for manufacturing fluorinated polymers comprising PFPE segments and fully hydrogenated segments, said process being conveniently applicable on an industrial scale and allowing to modulate the molecular weight and the structure of the resulting fluorinated functional polymers and to obtain monofunctional PFPE with satisfactory yields. It would also be desirable to provide methods for transforming the polymers into further functional derivatives.